A bit of background -
I unfortunately have never developed the stick-to-it-iveness required to successfully make reeds. But I had the good fortune (or bad, as the case may be for prodding me to learn to make reeds) of having had Brad Angus make a clutch of excellent reeds for my Kirk Lynch chanter back in about 2003 or so. They sounded and played GREAT all these years!
Well, I am down to the last two that function reasonably well in all respects save that the 2nd octave E requires considerably more pressure than the back D on both reeds these days, or pretty much any other note for that matter - else there WILL be Godawful Shrieking. Even with the added pressure it is still somewhat unpredictable.
I know that this a heads-ups that it's about bloody time I learnt to make a good reed for my chanter, but whilst I steel myself to begin this Sisyphean endeavour, I am hoping that someone may have an idea as to how to quell the shrieking for the meantime so that I can at least play without setting my teeth on edge, and anyone else's unlucky enough to be in the room. (God Bless my wife).
I had read and tried a few tips in one of Pat Sky's more recent writings, to no avail. The truly aggravating thing is that with the lips open just right, the better of the two reeds has a very pleasing tone and is adequately responsive - save for that #^%# E.

Firstly, just play the reed for a while, even if it sounds terrible. Sometimes simply "warming up" the reed will improve tone/tuning etc.

Secondly, check the humidity. As it is winter, the in-door humidity level will probably be low. You want to make sure that the humidity is stable, and, (in my case) between 40% and 60%). If it is lower than that, get a small humidifier (the kind you use for babies' rooms) to get the humidity up closer to Spring/Summer levels.

Thirdly, make tiny adjustments to the bridle, and play the chanter for a few minutes before you decide whether the adjustment has helped or hindered the reed.

If nothing helps, then either learn to make your own reeds or get Brad back on the case.

Thank you PJ. Alas, I indeed have been attending to all the things you've mentioned. I have the added challenge of living at 7,300' elevation in New Mexico. While I can modify the humidity situation by placing a dampened piece of open-cell foam over the bellows hole (works quite well), The lack of atmospheric pressure at this altitude cannot be modified. When I play these reeds at lower elevation they are quite passable, and used to work decently up here as well.
Guess I'm just going to keep playing and tweeking, for the nonce.

My guess is the reed is resisting the 'jump' into the second octave. If it was a new reed I'd be thinking of sanding down a little more to get the right response. But if it is an older reed that previously did not have this problem, it could be that a small leak has developed somewhere along the side where the two blades meet, causing a loss of pressure. To correct this I would rub a tiny amount of glue stick paper glue along both sides of the reed from the binding to just below the lips level. This should fill in any little gaps. You could also apply some around the top of the binding just in case the leak is coming from there.

Have been using beeswax in the same office as gluestick. Can only imagine it to be as effective, and doesn't chance sticking the blades together.
I too, had thought leaks may be the culprit with these older reeds. They do indeed leak when I suck on the staple, but most every reed I've ever had seems to do this to some degree...